In recent years, it has become important that, for example, industrial devices, home electrical appliances, and automotive parts provide increased energy savings. Electrical power currently generated at domestic power stations such as thermal power stations, hydroelectric power stations, nuclear power stations, or wind power stations is mostly generated with a rotary electric machine (power generator). Further, more than half the amount of domestically used electrical power is consumed to drive rotary electric machines. These electromagnetic products use an iron core made of a soft magnetic material. Enhanced efficiency can be achieved by reducing the loss of the iron core. Moreover, it is demanded that the electromagnetic products also achieve cost reduction in addition to efficiency enhancement.
The rotary electric machines basically include, for instance, an iron core made of a soft magnetic material, a coil, and a permanent magnet. The loss of the rotary electric machines can be roughly divided into iron loss and copper loss. The iron loss is determined by the characteristics of the soft magnetic material. The copper loss is determined by the resistance value of the coil, that is, the packing factor of the coil, and can be reduced by making the structure of a winding compact. Efficiency enhancement can be achieved by designing, for instance, the shape and dimensions of the rotary electric machines in such a manner as to reduce the aforementioned losses. However, the characteristics of the material can be changed with a view toward efficiency enhancement.
Amorphous alloys have top-ranking low iron loss characteristics among the soft magnetic materials. However, the amorphous alloys are manufactured by forming an amorphous body through rapid cooling. Therefore, the amorphous alloys can only be manufactured in the form of a thin foil strip (ribbon-shaped). This makes it difficult to form the amorphous alloys as an iron core. Consequently, the amorphous alloys have not been used for the aforementioned electromagnetic products.
The amorphous alloys can be used, for instance, as a wound core. As the wound core can be configured simply by winding a foil strip, it is possible to compensate for amorphous alloys' disadvantages such as poor workability, thinness, and unhandiness. If the wound core is used as is for a motor without being cut for segmentation, it is suitable for a configuration such as an axial gap motor (axial gap rotary electric machine).
A basic structure of the axial gap rotary electric machine is described, for instance, in Japanese Unexamined Patent Application Publication No. 2005-287212. This structure includes a teeth portion and a yoke portion, and has only one opposed surface that is oriented in axial direction to contribute toward torque output. Further, as this structure causes magnetic flux to flow from the teeth portion to the yoke portion, it is necessary to use a soft magnetic material in consideration of a three-dimensional magnetic flux flow. To meet these requirements, it is necessary to use a powder magnetic core or other material whose magnetic properties exhibit three-dimensional isotropy. However, these materials have lower magnetic permeability than a commonly used silicon steel sheet, and suffer from significant iron loss. Therefore, the use of these materials makes it difficult to reduce the size of the axial gap rotary electric machine.
The above problem can be addressed by the use of a technology that forms an amorphous iron core with two opposed surfaces oriented in axial direction. However, this technology needs further improvement. More specifically, magnetic flux obtained from the surfaces of opposing magnets separated by a gap cannot be effectively attracted to the core because the core's cross-sectional area in a plane perpendicular to a winding axis remains constant in any axial cross section. Further, if a large coil winding space is used, a coil region becomes enlarged to increase the inter-teeth distance. This increases torque pulsation and changes the waveform of induced voltage from a sine wave to a substantially rectangular wave. It means that the coil winding space is limited to reduce the degree of freedom in design.
The present invention provides an axial gap motor that, allowing an iron core to effectively attract magnetic flux obtained from opposing magnets separated by a gap, addresses the above-described problem with the related art by decreasing torque pulsation and keeping induced voltage in the shape of a sine wave, and increases the degree of freedom in design. The present invention also provides a low-iron-loss (high-efficiency), low-cost axial gap motor and electromagnetic products in which a high-quality soft magnetic iron core is placed at an appropriate position.